Security of Blind Signatures Revisited

We revisit the security definitions of blind signatures as proposed by Pointcheval and Stern (J Cryptol 13(3):361–396, 2000). Security comprises the notions of one-more unforgeability, preventing a malicious user to generate more signatures than requested, and of blindness, averting a malicious signer to learn useful information about the user’s messages. Although this definition is well established nowadays, we show that there are still desirable security properties that fall outside of the model. More precisely, in the original unforgeability definition is not excluded that an adversary verifiably uses the same message m for signing twice and is then still able to produce another signature for a new message \(m'\ne m\). Intuitively, this should not be possible; yet, it is not captured in the original definition, because the number of signatures equals the number of requests. We thus propose a stronger notion, called honest-user unforgeability, that covers these attacks. We give a simple and efficient transformation that turns any unforgeable blind signature scheme (with deterministic verification) into an honest-user unforgeable one.     

Instantiability of RSA-OAEP Under Chosen-Plaintext Attack

We show that the widely deployed RSA-OAEP encryption scheme of Bellare and Rogaway (Eurocrypt 1994), which combines RSA with two rounds of an underlying Feistel network whose hash ( i.e., round) functions are modeled as random oracles, meets indistinguishability under chosen-plaintext attack (IND-CPA) in the standard model based on simple, non-interactive, and non-interdependent assumptions on RSA and the hash functions. To prove this, we first give a result on a more general notion called “padding-based” encryption, saying that such a scheme is IND-CPA if (1) its underlying padding transform satisfies a “fooling" condition against small-range distinguishers on a class of high-entropy input distributions, and (2) its trapdoor permutation is sufficiently lossy as defined by Peikert and Waters (STOC 2008). We then show that the first round of OAEP satisfies condition (1) if its hash function is t-wise independent for t roughly proportional to the allowed message length. We clarify that this result requires the hash function to be keyed, and for its key to be included in the public key of RSA-OAEP. We also show that RSA satisfies condition (2) under the \(\Phi \)-Hiding Assumption of Cachin et al. (Eurocrypt 1999). This is the first positive result about the instantiability of RSA-OAEP. In particular, it increases confidence that chosen-plaintext attacks are unlikely to be found against the scheme. In contrast, RSA-OAEP’s predecessor in PKCS #1 v1.5 was shown to be vulnerable to such attacks by Coron et al. (Eurocrypt 2000).     

A novel two-channel continuous-time time-interleaved 3rd-order sigma-delta modulator with integrator-sharing topology

This paper presents a 3rd-order two-path continuous-time time-interleaved (CTTI) delta-sigma modulator which is implemented in standard 90 nm CMOS technology. The architecture uses a novel method to resolve the delayless feedback path issue arising from the sharing of integrators between paths. By exploiting the concept of the time-interleaving techniques and through the use time domain equations, a conventional single path 3rd-order discrete-time (DT) ΔΣ modulator is converted into a corresponding two-path discrete-time time-interleaved (DTTI) counterpart. The equivalent CTTI version derived from the DTTI ΔΣ modulator by determining the DT loop filters and converting them to the equivalent continuous-time loop filters through the use of the Impulse Invariant Transformation. Sharing the integrators between two paths of the reported modulator makes it robust to path mismatch effects compared to the typical time-interleaved modulators which have individual integrators in all paths. The modulator achieves a dynamic range of 12 bits with an OverSampling Ratio of 16 over a bandwidth of 10 MHz and dissipates only 28 mW of power from a 1.8-V supply. The clock frequency of the modulator is 320 MHz but integrators, quantizers and DACs operate at 160 MHz.     

Tensor-based methods for high-power amplifier identification and predistortion linearization

Aligned with the recent revolution of smart cities concept, a lot of work has been done to support the education process in direct or indirect way. In countries like Lebanon, in which the choice of school does not depend on the residence location, parents are becoming more and more selective in the quality of schools they are choosing for their children. This fact may lead parents to choose a modern and good school even if it is far from their residence. On the other hand, and even if the school was close enough, the traffic congestion would make the on-feet journey of the kid to the school very risky. Driving children to school is a solution. However, it consumes a lot of time and effort each day in the morning and the afternoon. Hence, school buses are commonly used by all schools to take the student from and to his home. Nevertheless, waiting the bus each day to arrive is an exhausting and a time-wasting mission. In this paper we present a smart transportation system for school buses that helps in saving parents’ time, by avoiding waiting school buses in the morning and then in the afternoon to return kids back, especially with the increasing traffic jams at these hours. The proposed mobile and web application is designed to help parents, school and the bus to communicate automatically and easily via the application in order to detect kids’ arrival time. The bus application side will notify parents few minutes before its approaching to their homes. Furthermore, the system will allow parents to inform the school and hence the bus application side about the absence of their kid. The system has been efficiently and dynamically designed and implemented so it can be hosted and used by any school administration without the need to any major modifications. It has been tested on a summer school to prove its efficiency and marked an important positive feedback from the school and the parents’ sides.     

Multi-antenna Decode and Forward Relay Selection over Nakagami-m Fading Channels

This paper analyzes the performance of opportunistic relay under aggregate power constraint in Decode-and-Forward (DF) relay networks over independent, non-identical, Nakagami-m fading channels, assuming multiple antennas are available at the relay node. According to whether instantaneous Signal-to-Noise Ratio (SNR) or average SNR can be exploited for relay selection, two opportunistic relay schemes, opportunistic multi-antenna relay selection (OMRS) and average best relay selection (ABRS) are proposed. The closed form expressions of outage probability and error performance for binary phase shift keying (BPSK) modulation of OMRS and ABRS are determined using the moment generating function (MGF) of the total signal-to-noise ratio (SNR) at the destination. Simulations are provided to verify the correctness of theoretical analysis. It is observed that OMRS is outage-optimal among multi-antenna relay selection schemes and approaches the Beamforming (BF) scheme known as theoretical outage-optimal very closely. Compared with previous single-antenna Opportunistic Relaying (OR) scheme, OMRS brings remarkable performance improvement obtained from maximum ratio combining (MRC) and beamforming, which proves that multiple antennas at the relays could provide more array gain and diversity order. It also shows that the performance of ABRS in asymmetric channels is close to OMRS in the low and median SNR range.     

Interference Cancelling Codes for Ultra-Reliable Random Access

Combinatorial code designs (CCDs) are proposed as a means for achieving ultra-reliability in the random access channel. In contrast to traditional access protocols that use random repetition coding, we show that by uniquely allocating repetition patterns to users, successful reception may be guaranteed up to a number of simultaneously active users in small frame sizes. Such codes are particularly robust in the low activity region where mission-critical machine-type communication is expected to operate. We also present deterministic codes designed to work in conjunction with successive interference cancellation to further improve reliability. The optimal IC code for frames of 5 access slots is given. Unlike slotted ALOHA, it is shown to limit packet losses to well below the ultra-reliability threshold (10^?5). These error performance gains come at the cost of a strict limitation on the supported user population (11 users in the case of 5 slots). We therefore consider larger frames of 24 slots, and analyse heuristic, low-complexity CCDs with fixed repetition factors that support up to 2024 users. While these are sub-optimal IC codes, significant gains are still observed compared to random codes.     

Direction of arrival estimation via reweighted $$l_1$$ norm penalty algorithm for monostatic MIMO radar

In this paper, a reweighted \(l_1\) norm penalty algorithm for direction of arrival (DOA) estimation in monostatic multiple-input multiple-output radar is proposed. In the proposed method, exploiting the inherent multidimensional structure of received data after matched filtering, the singular value decomposition (SVD) technique of the data matrix is employed to reduce the dimension of the received signal. Then a novel weight matrix is designed for reweighting the \(l_1\) norm minimization by exploiting the coefficients of the reduced-dimensional Capon (RD-Capon) spatial spectrum. The proposed algorithm enhances the sparsity of the solution by the reweighted \(l_1\) norm constraint minimization, and the DOAs can be estimated by finding the non-zero rows of the recovered matrix. Owing to utilizing the SVD technique and the novel weight matrix, the proposed algorithm can provide better angle estimation performance than RD-Capon and \(l_1\)-SRACV algorithms. Furthermore, it is suitable for coherent sources and has a low sensitivity to the incorrect determination of the source numbers. The effectiveness and superior performance of the proposed algorithm are demonstrated by numerical simulations.     

A queueing model of an energy harvesting sensor node with data buffering

Battery lifetime is a key impediment to long-lasting low power sensor nodes and networks thereof. Energy harvesting—conversion of ambient energy into electrical energy—has emerged as a viable alternative to battery power. Indeed, the harvested energy mitigates the dependency on battery power and can be used to transmit data. However, unfair data delivery delay and energy expenditure among sensors remain important issues for such networks. We study performance of sensor networks with mobile sinks: a mobile sink moves towards the transmission range of the different static sensor nodes to collect their data. We propose and analyse a Markovian queueing system to study the impact of uncertainty in energy harvesting, energy expenditure, data acquisition and data transmission. In particular, the energy harvesting sensor node is described by a system with two queues, one queue corresponding to the battery and the other to the data buffer. We illustrate our approach by numerical examples which show that energy harvesting correlation considerably affects performance measures like the mean data delay and the effective data collection rate.     

A fuzzy logic based buffer management scheme with traffic differentiation support for delay tolerant networks

Delay tolerant networks (DTNs) are an emerging class of wireless networks which enable data delivery even in the absence of end-to-end connectivity. Under these circumstances, message replication may be applied to increase the delivery ratio. The requirement of long term storage and message replication puts a burden on network resources such as buffer and bandwidth. Buffer management is an important issue which greatly affects the performance of routing protocols in DTNs. Two main issues in buffer management are drop decision when buffer overflow occurs and scheduling decision when a transmission opportunity arises. The objective of this paper is to propose an enhancement to the Custom Service Time Scheduling traffic differentiation scheme by integrating it with a fuzzy based buffer ranking mechanism based on three message properties, namely, number of replicas, message size and remaining time-to-live. It uses fuzzy logic to determine outgoing message order and to decide which messages should be discarded within each traffic class queue. Results of simulation study show that the proposed fuzzy logic-based traffic differentiation scheme achieves improved delivery performance over existing traffic differentiation scheme for DTNs.